This invention relates to the recycling of roadway materials such as old surfacing, made up of aggregates coated with a bituminous binder, in the form of bituminous millings, and reused as asphalt-fines matrices in the paving industry.
Ordinarily, bituminous pavements are composite constructions consisting of aggregates coated with a bituminous binder, over a layer of a few centimeters. However, after a certain length of time, these surfacings undergo an aging caused by the constraints generated by traffic and weather conditions, which causes a hardening of the binder, the apparition of stress cracks and/or the phenomenon of rutting.
One must therefore plan for treatment of the road in order to remedy these degradations.
With this in mind, various recycling procedures have been implemented, using, among others, techniques that consist in milling the existing surfacing with a machine in order to obtain a material called "milling", that is then mixed with a regeneration bituminous binder according to a hot or cold process.
The conventional recycling of roadway materials, which has been the object of many works for several years, calls for a wide range of techniques adapted in particular to asphalt-fines matrices. These various procedures, developed by paving companies and now well mastered, use specific equipment for the recycling in plant or remixing in situ, and for bituminous materials, where the principal that is used is based on the notion of regeneration of the bitumen present in the layer to be treated and on the correction of the granulometric curve per supply of new aggregates and possibly of fines.
Concerning the bituminous binder, the objective is to regenerate the old bitumen, whose hardening is a result of the volatilization of its lighter parts, by correcting its chemical composition using a customized binder in order to obtain a final binder with the characteristics of a traditional bitumen. With this in mind, the oil companies are marketing recycling binders with an aromatic characteristic and low asphaltene contents.
These procedures use hot or cold techniques.
In particular, such a cold regeneration procedure is described in patent EP-0 286 531, that teaches the use of a regeneration binder consisting of a bitumen with a high penetrability and a high content in aromatic compounds, this binder contains approximately 10% of an essentially aromatic solvent, whose characteristics and implementation content are determined based on the characteristics of the aged coated material, in particular the nature of the aggregates, and the content and characteristics of the initial binder.
Furthermore, we also know, through European patent application EP-0 810 276, that we can use a procedure of bitumen recycling that consists in disintegrating old asphalt into particles smaller than 5 mm, and separating these particles into at least two fractions and heating them separately, before mixing them with new bitumen, for example in the form of an emulsion.
More recent developments have tried to partially resolve these problems by using on site cold reprocessed millings, either with cement, or by associating cement and bitumen emulsion, without however in some cases, obtaining a significant stiffness modulus.
This is the case in particular in German patent application DE-3 729 507, that relates to a procedure for recycling road bitumen by mixing aggregates obtained by disintegration of the surface layer with an aqueous bitumen emulsion in which is incorporated between 1 and 5% by weight of a hydraulic binder such as cement, in order to improve the mechanical resistance of the material.
Nevertheless, these procedures do not make it possible to eliminate the major technical constraint, which is the need to have homogenous millings, both from the granulometric and composition point of view and as far are the characteristics of aging binders are concerned, whose regeneration must be reached by mixing it with a new binder.
But this is a significant handicap for the management of the collection, sorting and storing of materials to be recycled that greatly reduces the economic interest of these traditional recycling procedures and has limited the development of recycling in France.